Relays have several important uses in electronics. A relay is powered by a small electric with the ability to turn a larger electrical current on or off, like a switch. Joseph Henry, an American electromagnetics scientist, is credited with creating the concept of switching large electromagnets on and off.
Relays can be utilized in different ways depending on what is needed. The most common uses include controlling heavy motors and being a tool in switch circuits. Relays can be used in home automation projects through microcontrollers to switch AC loads, to schedule a time or condition for a heavy load to turn on or off and can be used to disconnect a load from its supply in the case of fa failure as a safety precaution.
There is a relay for every event or use imaginable. There are electromagnetic relays, thermal relays, power varied relays, and multidimensional relays all ranging in size, use, and ratings. In this article we will be covering electromagnetic relays, solid state relays, hybrid relays, thermal relays, and reed relays.
Electromagnetic relays are made up of electrical, mechanical, and magnetic components with coil to mechanical contact points. When the coil gets stimulated by a supply system, the mechanical contacts open or closed like a gate.
Solid state relays use stationary components to perform a switching program. The control energy needed to power the relay is lower in comparison to the output power leads to a higher power gain when compared to electromagnetic relays. These relays also are equipped with photo coupled SSR where an LED control signal is detected by a photo-sensitive semiconductor device. This photo detector is used to trigger the TRIAC or SCR gates to switch the load.
Hybrid relays have two parts, electromagnetic relays and electronic components. Each relay contains and input and output part. The input part is made up of electronic circuitry while the output part includes the electromagnetic relay.
Thermal relays are affected by heat and can reflect temperature change by changing the position of the contacts through use of the temperature sensors. Their main use is in motor protection to prevent overheating and are also named thermal overload relays.
Reed relays are made up of two magnetic strips, called a reed, that is sealed within a glass tube. When a magnetic field is applied to the system, the reed moves to operate the switching mechanism.
Now most importantly, how do relays work? There are four structures to a relay: a frame, coils, armature, and contacts. When a coil is electrified by a current, the coil produces a magnetic field. Since the coil is now magnetic it now attracts a ferrous plate, which is a component of the armature. On one end of the armature, a metal frame allows the device to pivot. This will help facilitate the change from normally open (NO), where there is open contact for the relay to energize, to normally closed (NC), where there is close contact.